The present invention is directed to a flap valve with a flap pivotally mounted within an annular casing. The casing forms an opening for passage of a fluid through the valve. The casing is made up of two annular casing parts in contacting engagement with the plane of contact between them extending transversely of the axis of the opening through the valve. An annular seal is mounted in a slot formed by the two casing parts at the plane of contact.
In the patent publication DE-A1-No. 31 042 11, a similar flap valve is disclosed with the seal including arcuately extending seal members with a solid rectangular cross-section.
To obtain an effective seal and low torsional moment forces with the flap, the seal must be sufficiently flexible, that is, it must be formed of a soft sealing material and, as a result, is not wear-resistant. Such a sealing material is exposed to wear due to contact with the flap.